Method of making mark plates for micrometer oculars and mounting of the same



June 8,1926. 1,588,221

' W. BAUERSFELD METHOD OF MAKING MARK PLATES FOR MI CROMETER OCULARS AND MOUNTING OF THE SAME" Filed August 15, 1924 3 Sheets-Sheet 1 y \fi x F. e I x k e June 8 1926. 1,588,221

W. BAUERSFELD METHOD OF MAKING MARK PLATES FOR MIGROMETER OCULARS AND MOUNTING OF THE SAME Filed August 15, Z1924 3 Sheets-Sheet 2 June 8 1926. 1,588,221 w. BAUERSFELD IETHOD OF MAKING MARK PLATES FOR MICROMETER OCULARS AND MOUNTING OF THE SAME Filed August 15, 1924 3 Sheets-Sheet 5 these spirals rests upon a circle Patented June 8, .1926.

WALTHEB BAUERSFELD, OF JENA, GERMANY, ASSIGNOR TO FIRM OF CARL ZEISS, 7

PATENT OFFICE.

OF JENA, GERMANY.

METHOD MAKING MARK PLATES FOR MICBOMETER OCULARS'AND MOUNTING- THE SAME.

Application filed August 15, 1924, Serial No. 732,296, and. in Germany October 1, 1923. p

l lars. The present invention relates to such micrometer oculars in which a rotatable mark plate is fitted with a spiral, embracing the point of intersection of the axis of rotation with the plane of the mark as a '10 pole, which spiral is successively brought into coincidence with the image, adjusted on a radial ray, of the extreme points of the distance to be meausred, whereby the radial distance of the two spiral points coinciding withthe extreme points can be directly read oil on a circle-division fixed concentrically with the axis of rotation on the markplate itself. The present invention affords a method of making the mark plates 'and prevents the point of rotation of the plane of the mark from deviating from the pole of the spiral, and consequently the curve from having an eccentric error which might impair the result of measurement. The new method provides mark plates in 1 which the mark consists of several spirals embracing the axis of rotation of the mark plate in the point of rotation of the plane of the mark. Thereby the construction of whose radius may in a given case assume the limit zero) described about the point of rotation of the plane of the mark and they fulfil the condition that the distance of two adjoining windings measured on a pencil of tangents of this circle has a constant magnitude. For

it is by no means suitable that the mark is formed by a single spiral because, as is well known, it is difiicult to attain the exact coincidence of a point (e. g. an extreme point of the distance to be measured), which is as usual denoted by a line perpendicular to the distance to be measured, with a curve likewise represented by a line. If, however,

the curve be an imagined line, which bisects the distance between two real curves travelling beside each other at an invariable, comparatively short distance, the adjustment is possible in a much more exact man ner. The spirals which obey to' the said law may be represented by the following two equations related to a rectangular co-ordihate-system, the origin of which coincides single curve-points, form with the axis of I abscissas. Vhen using the curves characterized by the equations the position of the image of the distance to be measured during the measurement must be so chosen that this image falls upon one of the tangents is made by photographically transmitting I the mark by means of a double exposure from a pattern to the mark plate, whereby the mark plate is rotated between exposures through 180 about the same axis of rotation about which it is to be subsequently rotated with the rotations taking place for measuring purposes in the micrometer ocular. Thereby the pattern is provided with two spirals, of which the one has originated from the other by means of rotation about the centre of the circle, on which its construction rests, through an angle deviating a little from 180. Hence, there arise on the mark plate two double spirals which are congruent to each other and each of which bisects the interval between thewindings of the other one. As, however, one onlyrequires one double spiral for the measurements, one can suitably cover with the twofold transmission of the pattern to the mark plate in the one position of the latter the one spiral and in the other position the other spiral. In the. event of an eccentric error both curves forming the double spiral would be uniformly displaced in opposite direction, viz, by the amount of the eccentricity relatively to their correct position and consequently the width of the interval between the double lines would vary. However, a simple consideration shows that the curve bisecting the interval itself is again aspiral congruent to the two spirals forming the double curve with which the centre of the circle, on which its construction rests, bisects the connecting line of the two centres of the circle appertaining to the two spirals of the double curve. Thereby it is achieved that with this imagined curve, which is actually used for the measurement, the eccentric error is eliminated. I

For the use in micrometer oculars it is suitable to select from the number of the available spirals those, whose'construction can be'carried out as exactly as possible with the simplest possible means in order that the pattern, serving as a base for making themark plate, is not afilicted already with objectionable defects. Such curves of simplified construction result if in the equations 1) fice the simplest means since the measurement isnot impairedby back lash between the actuating member and the mark plate. Special care must, however, be used for the bearing and guide of the mark plate. The usual construction with a cylindrical guidepivot, guided in a likewise cylindrical bearing, is not to be recommended owing to the unavoidable defects connected therewith through the play which always exists between the two elements.- According to the invention it is possible to provide micrometer oculars with a rotatable mark plate made after the above described method which mark plate is actuated by a friction wheel and guided by a ball held by a bearing fixed on the micrometer ocular and engaging into a recess of the mark plate in such. a way that its centre lies in the plane of the mark.

In the annexed drawing Figs. 1 and 2 show examples of the curves corresponding to the equations (1) and (2), (5) and (6) as well as (7) and (8).

Figs. 3 to 8 represent a constructional example of anmicrometer ocular provided with a rotatable mark plate. according to the invention. Fig. :3; shows partly in a cross section the micrometer, ocular in elevation, ,Fig. 4' shows .a plan .elevatlona section on the l ne 4-4. of Fig'. 3.

Fig. 5 shows "a top view of the rotatable mark plate and Fig. 6 represents on an enlarged scale'the image perceived by the observer in the ocular with an optional osition of the mark plate.- Fig. 7 is a great y enlarged top view of a pattern available for making the rotatable mark plate and Fig. 8 is on the same scale a top view of an unfinished mark plate made with this pattern by photographic process and with which the exposures are assumed. to be made without covering a part spectively as shown in the drawing. By oa and a. respectively are denoted the angles .which the normals of the tangents of a circle appertaining to optional curve-points P and P respectively form with the axis of abscissas. An Archimedean spiral s (Fig. 2) corresponds as the second special case to the equations (7) and (8) and has a parameter a of a magnitude a as shown in the drawing. As hereby r O, the tangents of the circle on which the construction of the curve is based appear as radial rays through the zero point of the coordinates, whereby a denotes the angle formed by the normal on the radial ray appertaining to an optional curve-point P, with the aims of abscissas'.

In the example illustrated in Figs. 3 to 8 there is screwed by means of a threaded tube 0 on an ocular tube Z) (Figs. 3 and 4) fitted with two ocular lenses 6 and Z) a casing 0 for a rotatable, circular mark plate of glass d. The casing 0 is closed with a lid f which is provided with a threaded tube 7 in order to be able to fix the micrometer ocular on an optical observation instrument. ()n the lid 7' are also provided two bearings g and g in which are supported two rollers 71. and k which carry conjointly with a driving-pulley i the mark plate d. The latter is pierced at its centre at al and a ball A: which is ground at this place in the mark plate 03 up to the depth of half the diameterof the ball and which, on the other hand, rests in a conical bearing 0 of the casing 0, serves for guiding the mark plate d. The top surface (vide the drawing) of the mark plate cl lies in the front focal plane of the ocular and must during the use of the ocular simultaneously lie in the rear focal plane of the imaging system of the optical observation instrument. In the threaded tube 0 there is disposed a second, fixed mark plate Z in such a way that its bottom surface (vide the drawing) .lies close to the rotatable mark plate d.

This surface carries an index an (F i'g. (3) and two semi-transparent diaphragm surfield of VlQW. For actuating the drivingpulley a which is fixed on a bolt 0 serves "faces n and n which partly" cover the I a milled head 2. The rotatable mark plate d (Fig. 5) carries an Archimedean double spiral and a circle-division 15, whose centre lies with the pole of the spiral g in the axis of the bore d and with'which the index-m coacts. A pattern plate at (Fig. 7) is' provided with two uniform Arch'imedean spirals 8 and 0' with a joint pole, of which the one almost bisects, but not exactly, the interval of the windings of the other one. A mark plate d with copies s 8 and 0' 0 of the two spirals 8 and 0, for the manufacture of which by means of a twofold exposure on the mark plate rotated through 80 the pattern u is suitable, is shown in ig. 8. i

The method of making the mark plate illustrated in constructional example is as follows. On a pattern-plate it one makes at first two uniform Archimedean spirals 8 and 11 by bringing the exactly drawn spiral 80 into the position 0 by means of rotation about its pole through an angle deviating but little from 180. After the spiral 0 has been covered, a photographic exposure of the pattern u is made on a suitable mark plate d. Thereupon the spiral 80 is covered instead of the spiral and a second exposure made on the mark plate d after the same has been rotated through exactly 180, whereby as a guide during this rotation the ball is was used which was placed into the bore (1 corresponding to the pole of the spiral-image s first photographed. The mark plate 65 is therefore rovided with the spiral-images s and 0 which form the double spiral q. Moreover, the graduation t is traced in an optional way upon the mark plate d. The manufacturer of a mark plate with curves which obe' to the equations (1) and (2') or (5) an (6) is the same except that instead of the Archimedean spiral one of the above mentioned curves is first traced upon the pattern-plate u.

.The measuring process with the micrometer ocular as illustrated consists in this that both extreme points of the distance to be measured, which is imaged in the plane of the mark by the imaging system of the observation instrument, are successively brought, by rotating the milled head p, into such a position relatively to the double spiral 9 that they bisect the interval between the two lines. The difference between the values read ofi on the index m and the graduation t for these two adjust-' ments of the rotatable mark plate (l indicates with a corresponding gauging of the graduation t the length sought of the distance to be measured. It is, of course, just aswell possible to' carry out measurements with a mark plate provided with two double spirals, during the manufacture of which none-of the single curves is covered. Such mark plates require, however, a double graduation, each of which extends to half a circumference of the mark plate. hen using Archimedean spirals, the two semitransparent diaphragm surfaces are to be so disposed that the intermediate strip which is not cut oil' from the light is in radial direction tothe point of rotation of the mark plate d. When using the involute or the curve represented by the equations (1) and (2) as a measuring curve, this strip ought to lie on the place of-the mark tangentially onthe circle upon which the construction of the measuring curve is based. The cutting down of the light has for its object to confine the space of measuresisting in tracing two congruent spirals on an-auxiliary plate, each of these spirals being related to a circle in such a way that the distance of two adjoining windings of the spiral as measured on a pencil of tangents of the circle, has a constant magnitude, and the two spirals being so traced that the two appertaining circles coincide with each other and the one spiral is rotated relatively to the other through an angle differing but little from 180, and then in twice photographically transmitting the auxiliary plate to the mark plate, and rotating the mark plate in its plane about its centre through 180 between the two exposures.

2. Method of making rotatable mark plates destined for micrometer oculars, consisting in tracing two congruent spirals on an auxiliary plate, each of these spirals being related to a circle in such a way that the distance of two adjoining windings of the spiral as measured ona penc1l of ten gents of the circle, has a constant magnitude, and the two spirals being so traced that the two appertaining circles coincide with each other and the one spiral is rotated relatively to the other through an angle differing but little from 180, then covering one spiral and photographically transmitting the other spiral from the aux-s iliary plate to the mark plate, then .rotating the mark plate in its plane through from the auxiliary plate to the mark plate.

3. Method of making rotatable mark plates destined for micrometer oculars, consisting 1n tracing two congruent spirals on an auxiliary plate, each of these spirals being related to a circle in such a way that the distance of two adjoining windings of the spiral asmeasured on a pencil of tangents of the circle,.has a constantjmagnitude, and ,the two spirals being so traced that. the two appertaining circles coincide with each'other and the one spiral is rotated relatively to the other through an angle difi'ering but'little 'from 180,in the fitting on a mark plate a bearingdevice allowing of rotating the mark plate in its plane, and then in twice photographically transmitting I the auxiliary plate to the mark plate in such a way-that the common centreof said circles falls into the-axis of the bearing device, and rotating the mark plate in its plane about the saidbearing device through 180 between'the two exposures.

4.-Method of making rotatable mark plates destined formicrometer oculars, conthrough 180 between the two exposures.

5. The combination of a casing fitted with a fastening device, adapted to fix the casing on an optical observation instrument, a transparent plate provided with measuring marks and disposed within the casing, a ball inserted between the centre of the plate and the casing, a bearing device keeping the plate,the ball and the casing in contact with each other, a friction disc, rotatably supported in the casing and coasting with the plate, an actuating device con- I nected to the friction disc, and an ocular fixed on the casing and allowing of 0bserving the plate.

Y 6. The combination of a casing fitted with a fastening device, adapted to fix the casing on an optical observation instrument, a

'transparent'plate provided with measuring marks and disposed within the casing, a ball inserted between the centre of the plate and the casing, two rollers, rotatably supported in the casing and acting upon the face of the said plate, opposed to the said ball, a friction disc, rotatably supported in the casing and acting on the same face of the plate as the said rollers, the rollers and the friction disc cooperating to keep. in contact the plate and the'ball, and an ocular fixed on the casing and allowing of observing the plate.

WALTHER BAUERSFELD. 

